I'm having about the same thing as this guy but mine is a2.8 mine is sputtering and missfiring under a load. I have changed everything from fuel pump filters timing carb adjustments accelerater pump power valve wires plugs grounds and so on still can't find the problem
Welcome to TRS
Whats the spark timing set at?
And are you using the TFI module spark system?
There are two spark advance/retard methods that need to be used on all gasoline engines, except fix speed/RPM engines
RPM advance/retard
LOAD advance/retard
14.7:1 air fuel ratio burns at a fixed rate, and its not instant, lets say from Spark to full explosive power takes 500 milliseconds(made up number)
So spark ignites the fuel Before TDC so full explosive power happens 10deg AFTER TDC so it can push piston down to add power to the crank, too far after TDC and little power it added, to close to TDC and damage can occur because there is no leverage to push piston down, so piston or rod can be damaged, before TDC and engine stops, lol
At idle 700rpms, a piston moves from 10deg BTDC to 10deg ATDC in say 500ms
So base timing is set at 10deg BTDC, spark happens then 20deg later full explosive power
But at 1,400 RPMs piston is moving twice as fast, so spark has to happen at say 20deg BTDC
At 2,800rpm 30deg BTDC
This is what RPM advance/retard does
RPM advance in a distributor setup was done with "weights and springs" inside the distributor
As the shaft inside the distributor spins faster with higher RPMs the weights move "out" away from the shaft and that advances the spark timing, as shaft slows the springs pull the weights back "in" retarding the spark timing
Weights and springs are changeable/adjustable to fine tune for best RPM spark timing
LOAD is a different kettle of fish
When you make the air:fuel ratio Richer the time from spark to full explosive power is shorter, so instead of 500ms its now 400ms
And RPM spark timing is now incorrect
Thats is what Vacuum Advance was for, when you accelerate more fuel is added, Richer mix, and intake manifold vacuum drops because throttle plate opens more
So Vacuum advance retards the RPM advance for the shorter burn time of the Richer mix
If that doesn't happen then engine stumbles and misfires
When car makers went to computer controls for spark they dropped vacuum advance in favor of computer advance
RPM advance usually stayed as is until distributorless spark systems were used
TFI used a SPOUT wire between computer and distributor
This SPOUT wire needs to be disconnected to set base spark timing, RPM timing, at 10-12deg BTDC
Then reconnected so you have LOAD advance back